Dust and Molecules in primordial galaxies

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Dust and Molecules in primordial galaxies

• F.-Xavier Désert, Lab. Astrophysique, Grenoble
• Erik Elfgren, Dept. of physics, Lulea, Sweden

Early dust in the galaxy structure formation
opens up the possibility that Normal but
intense star formation occurred in the first
large galaxies. Normal molecular H2 formation on
dust. Here, we focus on z 20 to 5 dark age
period, preceding the IR bright, star formation
peak at z 3-1
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WMAP One year
Temperature - Polarization Correlation ?
0.17?0.04
Bennett, et al., 2003, ApJSS
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Early reionisation suggested by WMAP

• TE correlation at low l suggests Reionisation
  redshift of zi 15
• Pop III stars are likely the source of the UV
  ionizing radiation field
• Could also produce some dust that will
  disseminate in the intergalactic medium (SNe and
  stellar winds can expel matter from low mass
  galactic halos).
• UV and dust altogether make an infrared
  background, which is computed here, that can be
  constrained by FIRAS Cosmic Infrared Background.
• Elaboration on early works by e.g.
  Bond,Carr,Hogan '91

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Dust Production and Destruction

• Assumes a fraction (0.1) of the baryons consumed
  in stars re-emerges as dust. The UV background
  implies a baryon consumption rate (36 eV/ 7 MeV
  baryons for one UV photon)
• Empirical lifetime is introduced based on
  (limited) knowledge of the Milky Way (0.1 Gyr)

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Comoving dust density evolution
Direct consequence from UV background Cen 2002,
ApJ
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Dust Opacity
_at_1mm
In the (sub)mm mostly in n²
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Dust temperature
Radiation field is much smaller than the
CMB Tdust gtTcmb
is just above the CMB temperature
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Submillimetre Background Generic spectrum
Planck HFI bandpass
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• Planck (August 2007)
• should help find small scale structure of this
  submillimetre background.
• Component separation on HFI maps could yield an
  unambiguous trace of early dust in the
  reionization period.

Need for N-body simulations including the dust
component (in progress with B. Guiderdoni and E.
Hivon)
Jenkins et al, 1998 ApJ, 499, 20
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Consequences

• This early dust can provide the seeds for the
  formation of molecules
• These molecules will then make the star formation
  efficient at z 1-3, the major star producing
  event in the Universe.
• Planck will put strong constraints on this
  scenario (submillimetre capabilities of HFI).
• In theory, there is no difference between theory
  and practice. In practice, there is. (Chuck Reid)

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Star formation history
Gispert et al. 2000, AA
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Pierre Encrenaz

• Dark baryonic matter
• Dark matter
• Dark energy
• Dark Pierre his influence on French Astronomy
• String theory
• Acoustic peaks in the CMB the cosmic drum
• Thanks for the practice of 16 strings and the 7
  last words (Haydn).